The clamp device is widely used in a welding process of an automatic assembly line of the machine industry and the like. A clamp device of this type generally has a pair of clamp arms rotatably mounted on a clamp body via pins. By applying a driving force of a cylinder to one end portion of each clamp arm, these clamp arms are rotated about the pins, and a workpiece is clamped and positioned from the left and right sides by a gripping surface provided at the other end portion of each clamp arm. Then, the workpiece is subjected to necessary processing and a transportation process (see, for example, Japanese Patent No. 4950123).
Among those clamp devices, for example, Japanese Laid-Open Patent Publication No. 2015-037829 discloses a clamp device in which a pair of clamp arms having attachments attached to the gripping surfaces and a pair of clamp arms having no attachment attached to the gripping surfaces are selectively rotated.
In addition, Japanese Laid-Open Patent Publication No. 2009-012138 discloses a clamp device that clamps a workpiece by translating a pair of clamp arms in a direction to approach or separate from each other.